Quantifying passive and forced airflows through the subway platforms of Dortmund (Germany)

Information about systems of currents and air flow in underground public transport is scarce, especially when such information should be accessible to the public; thus, conditions of how pollutants spread within tunnels and stations of such an underground system are not known very well. Such sufficient and detailed knowledge about the „underground“ field of air flow and its interactions with the urban atmosphere outside is important to provide an effective prevention of illnesses, when it comes to bioclimatic and hygienic problems with air pollution; to take effective measures in situations where evacuation is necessary (e.g. fire); such knowledge is urgently needed.

The gas attack of the underground system of Tokyo has raised world-wide concern about terrorist ac-tivities in tunnel systems (e.g. underground transportation) and effective prevention and evacuation measures. Due to the facts, that many people are concentrated in a very small area, that pathways for pollutants or gas are restricted, and that dispersion effects are very low as well as its decay is slowed down, underground systems of public transport are especially prone to terrorist activities. Ways in which such pollutants spread are only little known yet; especially if active ventilation is absent these ways of spreading are highly dependent on weather conditions outside the underground system especially in the vicinity of exits and entrances where interactions between the “atmosphere” inside and outside the underground system are manifold; thus, annual and seasonal variability of the weather has an influence as well which must not be underestimated.

From these dependencies between outer and inner atmosphere mentioned above as well as local modifications, complicated and manifold interactions can be deduced that are still largely unknown and have to be studied. Knowledge in this area is highly needed in order to be able to predict and prevent the impact of air pollutants, possible gas attacks and fires as well as to be able to evacuate people as soon as possible. Studies so far have been very scarce which is the reason for increased need of investigations. Due to this fact, we have measured climatic conditions in the subway systems of New York City since the summer of 1998 (in co-operation with the Hunter College of City University of New York). Based on the experiences gained in these investigations, a comparable measurement plan was made for the Underground public transport (U-Bahn) in Dortmund, Germany. Main focus of this investigation as well as in New York City is on local currents and air exchange conditions in the inner areas of the stations and the direct interactions with the urban atmosphere. In this context, controls and laws governing the directions of currents in its dependency on wind speed, and direction and strength of vertical air flow at different temperature gradients are of particular interest. The presentation of first results from New York City as it has already taken place in November 1999 in Sydney at the International Conference on Urban Climatology will be continued here with first re-sults of the measurements from Dortmund.